White balance adjusting device for a color video camera

Abstract

A white balance adjusting device for a color video camera detects a color temperature detection signal R-B and a color information signal R+B-2Y from a video signal provided by the color video camera. A control signal generating means of the white balance adjusting device generates a control signal to drive a gate circuit when the level of the color information signal R+B-2Y is within a predetermined range of level. When the level of the color information signal is within the predetermined range of level, the gate circuit passes the color temperature detection signal R-B to apply the color detection signal R-B to a clipping circuit. The clipping circuit clips the amplitude of the color temperature detection signal R-B within a predetermined range of level. Chrominance signal gain control circuit for controlling the gains of chrominance signals R and B is controlled by the output of the clipping circuit for white balance adjustment.

What is claimed is: 
     
       1. A white balance adjusting device for a color video camera, comprising: a first detecting means for detecting color temperature variation on the basis of a video signal provided by the color video camera;   a chrominance signal gain control means which is controlled for controlling the gain of chrominance signals by a detection signal provided by the first detecting means;   a second detecting means for detecting color information from the video signal;   a first output means which decides whether the level of the detection signal provided by the second detecting means is within a first range, and provides a first control signal; and   a control execution means which enables the control of the chrominance signal gain control means by the detection signal provided in accordance with the first detecting means by the first control signal, when the level of the detection signal provided by the second detecting means is in the first range.   
     
     
       2. A white balance adjusting device according to claim 1, wherein said first output means comprises a pair of comparing means for deciding whether the detection signal provided by said second detecting means is within said first range, and logic circuit means for producing said first control signal by processing the outputs of said pair of comparing means. 
     
     
       3. A white balance adjusting device according to claim 2, wherein said first detecting means includes a limiting means for limiting the effective range of detection of color temperature variation. 
     
     
       4. A white balance adjusting device according to claim 3, wherein said limiting means is a clipping circuit which limits the amplitude of said detection signal within a predetermined range of level. 
     
     
       5. A white balance adjusting means according to claim 1, wherein said first detection signal is an R-B signal, where R is a red signal and B is a blue signal. 
     
     
       6. A white balance adjusting device according to claim 1, wherein said second detection signal is an R+B-2Y signal, where Y is a luminance signal. 
     
     
       7. A white balance adjusting device according to claim 1, wherein said second detecting means comprises a plurality of color information generating means for generating color information corresponding to the level of the detection signal provided by said first detecting means, and selecting means for selecting the outputs of the color information generating means. 
     
     
       8. A white balance adjusting device according to claim 7, wherein said color information generating means are two adding means differing from each other in addition ratio, respectively for receiving the two pieces of color information produced on the basis of said video signal. 
     
     
       9. A white balance adjusting device according to claim 1, further comprising: a second output means which decides whether the level of the detection signal provided by said second detecting means is within a second range of level, and provides a second control signal; and   a control mode varying means for varying the mode of control operation of said control execution means according to said second control signal.   
     
     
       10. A white balance adjusting device for a color video camera, comprising: a first detecting means which detects the variation of the color temperature of a lighting source on the basis of a video signal provided by the color video camera and provides a color temperature variation signal;   a second detecting means which detects color information from the video signal and generates a chromatic color discriminating signal;   a control signal generating means which decides whether the level of the chromatic color discriminating signal provided by the second detecting means is within a predetermined range of level, and generates a control signal;   a gate means which gates the output of said first detecting means according to the control signal provided by the control signal generating means;   an amplitude limiting means for limiting the amplitude of the output of the gate means below a predetermined amplitude; and   a gain control means which controls the gains of the chrominance signals of the video signal according to the output of the amplitude limiting means.